Incidentally, I picked up this definition of ultra-leftism or left-opportunism from a pamphlet written by an Australian and originally published by The Communist Party of Australia. It was reprinted in the U.S. by the Communist Labor Party - it is a glossary of Marxist terminology. I have it around the house someplace but it got misplaced and I can't put my hands on it.
^^^^^ CB: "Ultra-left" or "phony-left" are contemporary synonyms for "Leftwing Communism" from Lenin's _Leftwing Communism: an Infantile Disorder_ . Lenin may be having fun with the Freudian term "infantile", fresh at that time. Lenin's book details the immature thinking (refusal to compromise on non-principled questions, etc.) of a number of "ultra-left" Communists in that period. Lenin also wrote a lot about petit bourgeois revolutionism.